[Bugfix][Rust Frontend][Renderer] Align DeepSeek V4 historical developer message handling (#54854)
Signed-off-by: reidliu41 <reid201711@gmail.com>
Reid committed
Sep 3, 2026 at 04:43 UTC
60857baa53a743913d4e919f12b5fd8d608ded86
2 files changed
+162
-7
rust/src/chat/src/renderer/deepseek_v4/encoding.rs
+40
-6
@@ -57,6 +57,8 @@ pub(super) fn render_request(request: &ChatRequest) -> Result<String> {
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let synthetic_tool_system = needs_synthetic_tool_system(request, request_tools);
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let drop_thinking = request.parse_template_bool("drop_thinking")?.unwrap_or(true)
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&& !rendered_tools_present(request, request_tools);
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+ let drop_historical_developers = thinking_mode == ThinkingMode::Thinking && drop_thinking;
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+ let last_user_like_message_index = request.messages.iter().rposition(is_user_like_entry);
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let last_user_render_index =
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find_last_user_render_index(request.messages.as_slice(), synthetic_tool_system);
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let mut out = String::from(BOS_TOKEN);
@@ -81,6 +83,12 @@ pub(super) fn render_request(request: &ChatRequest) -> Result<String> {
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let current_render_index = render_index;
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render_index += 1;
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86
+ if drop_historical_developers
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+ && is_historical_developer(message, message_index, last_user_like_message_index)
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+ {
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+ continue;
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+ }
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+
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match message {
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ChatMessage::System { content } => {
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let tools = if !request_tools_attached {
@@ -126,7 +134,12 @@ pub(super) fn render_request(request: &ChatRequest) -> Result<String> {
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}
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if (is_user_like_entry(message) || matches!(message, ChatMessage::System { .. }))
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- && next_rendered_entry_is_assistant_or_end(request.messages.as_slice(), message_index)
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+ && next_rendered_entry_is_assistant_or_end(
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+ request.messages.as_slice(),
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+ message_index,
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+ drop_historical_developers,
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+ last_user_like_message_index,
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+ )
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{
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write_assistant_transition(
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&mut out,
@@ -243,14 +256,35 @@ fn is_user_like_entry(message: &ChatMessage) -> bool {
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)
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}
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+/// Return whether a developer entry precedes another user-like turn.
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+fn is_historical_developer(
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+ message: &ChatMessage,
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+ message_index: usize,
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+ last_user_like_message_index: Option<usize>,
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+) -> bool {
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+ matches!(message, ChatMessage::Developer { .. })
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+ && last_user_like_message_index.is_some_and(|last_index| message_index < last_index)
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+}
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+
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/// Return whether the next rendered entry is assistant, or there is no next
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/// entry.
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-fn next_rendered_entry_is_assistant_or_end(messages: &[ChatMessage], message_index: usize) -> bool {
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+fn next_rendered_entry_is_assistant_or_end(
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+ messages: &[ChatMessage],
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+ message_index: usize,
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+ drop_historical_developers: bool,
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+ last_user_like_message_index: Option<usize>,
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+) -> bool {
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let mut next_index = message_index + 1;
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- if is_user_content_entry(&messages[message_index]) {
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- while next_index < messages.len() && is_user_content_entry(&messages[next_index]) {
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- next_index += 1;
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- }
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+ while next_index < messages.len()
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+ && (is_following_user_content(messages, next_index)
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+ || (drop_historical_developers
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+ && is_historical_developer(
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+ &messages[next_index],
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+ next_index,
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+ last_user_like_message_index,
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+ )))
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+ {
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+ next_index += 1;
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}
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290
messages
rust/src/chat/src/renderer/deepseek_v4/tests.rs
+122
-1
@@ -10,7 +10,7 @@ use super::DeepSeekV4ChatRenderer;
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use crate::ChatRenderer;
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use crate::event::{AssistantContentBlock, AssistantToolCall};
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use crate::renderer::test_utils::{FixtureRequestOptions, fixture_chat_request};
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-use crate::request::{ChatMessage, ChatRequest, GenerationPromptMode, ReasoningEffort};
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+use crate::request::{ChatMessage, ChatRequest, ChatTool, GenerationPromptMode, ReasoningEffort};
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fn render_request(request: &ChatRequest) -> String {
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DeepSeekV4ChatRenderer::new()
@@ -21,6 +21,19 @@ fn render_request(request: &ChatRequest) -> String {
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.expect("deepseek v4 renderer should return text prompt")
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}
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+fn thinking_request(messages: Vec<ChatMessage>) -> ChatRequest {
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+ let mut request = ChatRequest {
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+ messages,
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+ ..ChatRequest::for_test()
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+ };
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+ request
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+ .chat_options
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+ .template_kwargs
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+ .insert("thinking".to_string(), Value::Bool(true));
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+ request.chat_options.reasoning_effort = Some(ReasoningEffort::Low);
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+ request
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+}
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+
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fn fixture_request(input_name: &str) -> ChatRequest {
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let mut request = fixture_chat_request(&fixture_path(input_name), deepseek_fixture_options());
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request.chat_options.reasoning_effort = Some(ReasoningEffort::Low);
@@ -71,6 +84,114 @@ fn renders_developer_tools_like_hf_python() {
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);
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}
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+#[test]
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+fn drop_thinking_removes_developer_before_last_user() {
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+ let request = thinking_request(vec![
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+ ChatMessage::developer("old instruction", None),
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+ ChatMessage::assistant_blocks(vec![
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+ AssistantContentBlock::Reasoning {
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+ text: "old reasoning".to_string(),
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+ },
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+ AssistantContentBlock::Text {
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+ text: "old answer".to_string(),
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+ },
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+ ]),
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+ ChatMessage::user("next question"),
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+ ]);
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+
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+ let rendered = render_request(&request);
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+
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+ expect![
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+ "<｜begin▁of▁sentence｜>old answer<｜end▁of▁sentence｜><｜User｜>next question<｜Assistant｜><think>"
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+ ]
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+ .assert_eq(&rendered);
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+}
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+
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+#[test]
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+fn dropped_developer_does_not_hide_following_assistant() {
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+ let request = thinking_request(vec![
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+ ChatMessage::user("old question"),
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+ ChatMessage::developer("old instruction", None),
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+ ChatMessage::assistant_text("old answer"),
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+ ChatMessage::user("next question"),
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+ ]);
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+
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+ let rendered = render_request(&request);
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+
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+ expect![
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+ "<｜begin▁of▁sentence｜><｜User｜>old question<｜Assistant｜></think>old answer<｜end▁of▁sentence｜><｜User｜>next question<｜Assistant｜><think>"
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+ ]
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+ .assert_eq(&rendered);
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+}
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+
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+#[test]
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+fn drop_thinking_keeps_last_developer() {
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+ let request = thinking_request(vec![
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+ ChatMessage::user("old question"),
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+ ChatMessage::assistant_text("old answer"),
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+ ChatMessage::developer("latest instruction", None),
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+ ]);
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+
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+ let rendered = render_request(&request);
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+
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+ expect![
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+ "<｜begin▁of▁sentence｜><｜User｜>old question<｜Assistant｜></think>old answer<｜end▁of▁sentence｜><｜User｜>latest instruction<｜Assistant｜><think>"
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+ ]
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+ .assert_eq(&rendered);
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+}
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+
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+#[test]
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+fn drop_thinking_false_keeps_historical_developer() {
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+ let mut request = thinking_request(vec![
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+ ChatMessage::developer("old instruction", None),
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+ ChatMessage::assistant_text("old answer"),
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+ ChatMessage::user("next question"),
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+ ]);
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+ request
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+ .chat_options
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+ .template_kwargs
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+ .insert("drop_thinking".to_string(), Value::Bool(false));
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+
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+ let rendered = render_request(&request);
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+
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+ assert!(rendered.contains("<｜User｜>old instruction"));
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+}
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+
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+#[test]
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+fn drop_thinking_removes_developer_before_tool_response() {
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+ let request = thinking_request(vec![
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+ ChatMessage::developer("old instruction", None),
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+ ChatMessage::assistant_text("old answer"),
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+ ChatMessage::tool_response("result", "call-1"),
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+ ]);
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+
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+ let rendered = render_request(&request);
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+
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+ expect![
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+ "<｜begin▁of▁sentence｜>old answer<｜end▁of▁sentence｜><｜User｜><tool_result>result</tool_result><｜Assistant｜><think>"
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+ ]
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+ .assert_eq(&rendered);
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+}
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+
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+#[test]
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+fn tools_keep_historical_developer() {
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+ let tool = ChatTool {
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+ name: "lookup".to_string(),
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+ description: None,
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+ parameters: Value::Object(Default::default()),
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+ strict: None,
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+ };
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+ let request = thinking_request(vec![
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+ ChatMessage::developer("old instruction", Some(vec![tool])),
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+ ChatMessage::assistant_text("old answer"),
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+ ChatMessage::user("next question"),
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+ ]);
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+
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+ let rendered = render_request(&request);
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+
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+ assert!(rendered.contains("<｜User｜>old instruction"));
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+}
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+
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#[test]
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fn reasoning_effort_max_adds_prefix_when_thinking_is_enabled() {
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let mut request = ChatRequest {